water molecule
A molecule, consisting of one central oxygen atom and two hydrogen atoms along an angle of 104°, forming an electrostatic dipole because of the asymmetric distribution of charge.
The dipole results in a high dielectric constant for water, whether in vapor, liquid, or solid form. Resonances in the intermolecular bonds result in absorption and emission of electromagnetic radiation at near- and thermal-infrared wavelengths, hence the importance of water vapor in the greenhouse effect in the atmosphere and water substance as precipitation in the scattering and absorption of radar waves.
